i

FATIGUE LIFE PREDICTION ON HEAT TREATED LOW CARBON STEEL AND

ALUMINIUM

MOHD IHSAN BIN AB RAHIM

Report submitted in partial fulfillment of the requirements for the award of Bachelor of

Mechanical Engineering

Faculty of Mechanical Engineering

UNIVERSITI MALAYSIA PAHANG

JUNE 2012

vi

ABSTRACT

This research is to find the fatigue life prediction on low carbon steel and aluminum.

The objective of this project is to find the fatigue life of the different material which is

low carbon steel and aluminum. The second objective is to find out the effect of heat

treatment to the fatigue life of the material. The annealing and quenching heat treatment

is investigated in this research. The optical microscope and the fatigue test machine was

use in assisting for completing the research. The low carbon steel properties has the

higher strength compare to aluminum due to the higher fatigue life. The changing of the

microstructure due to heat treatment has changing the strength and surface fracture of

the material based on type of heat treatment. The annealing process have reduce the

strength of the material but the quenching process has increase the strength of both

material.

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ABSTRAK

Kajian ini adalah untuk mencari jangka hayat lesu pada keluli karbon rendah dan

aluminium. Objektif projek ini adalah untuk mencari hayat lesu bahan yang berlainan

iaitu keluli karbon rendah dan aluminium. Objektif kedua adalah untuk mengetahui

kesan rawatan haba kepada ramalan jangka hayat lesu bahan. Penyepuhlindapan dan

rawatan haba pelindapkejutan disiasat dalam kajian ini. Mikroskop optik dan mesin

ujian lesu adalah digunakan dalam membantu untuk melengkapkan kajian. Ciri-ciri

keluli rendah karbon mempunyai kekuatan yang lebih tinggi berbanding dengan

aluminium kerana jangak hayat lesu yang lebih tinggi. Perubahan mikrostruktur kerana

rawatan haba telah mengubah kekuatan dan keretakan permukaan bahan berdasarkan

jenis rawatan haba. Proses penyepuhlindapan telah mengurangkan kekuatan bahan tetapi

proses pelindapkejutan telah meningkatkan kekuatan kedua-dua bahan.

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TABLE OF CONTENTS

Page

TITLE PAGE i

APPROVAL PAGE ii

SUPERVISOR’S DECLARATION iii

STUDENT’S DECLARATION iv

ACKNOWLEDGEMENTS v

ABSTRACT vi

TRANSLATION OF ABSTRACT vii

TABLE OF CONTENTS viii

LIST OF TABLE xii

LIST OF FIGURES xiv

LIST OF SYMBOLS xv

LIST OF ABBREVIATIONS xvi

CHAPTER 1 INTRODUCTION 1

1.1 Project Background 1

1.2 Problem Statement 2

1.3 Objective 3

1.4 Scope of Project 3

CHAPTER 2 LITERATURE REVIEW 4

2.1 Introduction of Steel 4

2.2 Aluminum in Engineering 5

2.3 Microstructure of Steel 6

2.4 Heat Treatment 9

2.5 Hardening of Material 10

2.6 Introduction of Fatigue Life 11

2.7 Fatigue Background and History 11

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2.8 Fatigue Test 12

2.9 S-N Curve 13

2.10 Crack Growth Rates 14

CHAPTER 3 METHODOLOGY 16

3.1 Introduction 16

3.2 General Experiment Procedure 17

3.3 Material Properties 18

3.4 Specimen Preparation 19

3.5 Machining Material 22

3.6 Heat Treatment Process 24

3.7 Microstructure 26

3.8 Fatigue Testing 29

3.9 Fatigue Region Inspection 30

CHAPTER 4 RESULT AND DISCUSSION 32

4.1 Introduction 32

4.2 Microstructure Analysis 32

4.3 Fatigue Life Prediction on Heat Treated 36

Mild Steel

4.4 Fatigue Life Prediction on Heat Treated 39

Aluminum

4.5 The Comparison of Fatigue Life of Mild Steel 41

with the Different Heat Treatment Condition

4.6 The Comparison of Fatigue Life of Aluminum 43

with the Different Heat Treatment Condition

4.7 Comparison Fatigue Life of Different Material 44

with the Same Condition

4.8 Surface Features of Fatigue Fractures 47

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CHAPTER 5 CONCLUSION AND RECOMMENDATION 49

5.1 Conclusion 49

5.2 Recommendation 49

REFERENCES 50

APPENDICES 52

xi

LIST OF TABLES

Table

Page

2.1 Class of steel 5

2.2 Vickers microhardness of AISI 1020 10

3.1 Chemical composition of low carbon steel 18

3.2 Chemical composition of aluminum 19

3.3 Mechanical properties of low carbon steel 19

3.4 Mechanical properties of aluminum 19

3.5 Cutting speed 22

3.6 Feed based on material 23

3.7 Heat Treatment temperature table 25

3.8 Conditions of material 29

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LIST OF FIGURES

Figure

Page

2.1 Crystal lattice structure 7

2.2 Iron carbon phase diagram by mass 8

2.3 Microstructure as-receive of AISI 1020 9

2.4 Microstructure of the AISI 1020 steel heat treated 10

2.5 S-N diagram by Wholer 12

2.6 Curve for aluminum and low carbon steel 13

2.7 The Paris law for fatigue crack growth rates 15

3.1 Methodology flow chart 17

3.2 Band saw machine 21

3.3 Schematic diagram of raw specimen 21

3.4 Raw specimen of mild steel 21

3.5 Lathe machine 22

3.6 Schematic diagram 24

3.7 After machining 24

3.8 Heat treatment furnace 25

3.9 Grinding equipment 27

3.10 Polishing machine 27

3.11 Fume hood 28

3.12 Microscope 28

3.13 Fatigue test machine 29

3.14 Microscope 31

3.15 Analyze monitor 31

4.1 Low carbon Steel (a) 10x magnification (b) 20x magnification 33

4.2 Annealing mild steel (a) 10 x magnification (b) 20x magnification 34

4.3 Quenching mild steel (a) 10x magnification (b) 20x magnification 34

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4.4 Microstructure of (a) normal aluminum (b) anneal aluminum (c)

quenching aluminum with 20x magnification

35

4.5

4.6

Aluminum microstructure

S-N curve of normal low carbon steel

36

37

4.7 S-N curve for anneal low carbon steel 38

4.8 Quenching of low carbon steel 38

4.9 Normal condition of Aluminum 40

4.10 Annealing Aluminum 40

4.11 Quenching Aluminum 41

4.12 Comparison graph of different condition of mild steel 42

4.13 Comparison graph of different condition of aluminum 43

4.14 Normal mild steel Vs normal aluminum 45

4.15 Annealing mild steel Vs annealing aluminum 45

4.16 Quenching mild steel Vs quenching aluminum 46

4.17 Macroscopic surface features 47

4.17 Surface fracture of specimen 48

xiv

LIST OF SYMBOLS

Vf

Feed rate

f Feed

oC Degree Celsius

Fe Iron

C Carbon

Cr Chromium

Si Silicon

Mn Manganese

S Sulfur

Al Aluminum

Cu Copper

Mg Magnesium

��

�� Fatigue growth rate per cycle

K m

The stress intensity factor

ϭe Limit failure

µ Micro

xv

LIST OF ABBREVIATIONS

Pa Pascal

RPM Revolution per minutes

S-N Stress-Strain

CHAPTER 1

INTRODUCTION

1.1 PROJECT BACKGROUND

Steel is one of the most important material in our world. People mostly use steel

everywhere including in the construction, automotive industry or even in the daily

equipment manufacturing. Steel is a simply known as a material that consists of iron and

varying amounts of carbon. Iron is the major component in steel while carbon was their

excess between 0.2% to 2.14% depend on the grade. There 5 major classifications of

steel which is carbon steel, alloy steel, high-strength low-alloy steel, stainless steel and

tool steel (William et al,2005).

Different type of steel can be differentiate by the different in composition of the

carbon on the steel. The composition of carbon can be known by looking at the

microstructure of the steel. Carbon steel is defined as a steel that consist of various of

carbon, produce everything from machines to bedsprings to bobby pins (William et

al,2005). Carbon steel have 3 different types ; low carbon steel, medium carbon steel and

high carbon steel.

Low carbon steel has a composition of an iron alloy that contains less than 0.25%

carbon. Low carbon steel is very reactive and will readily revert back to iron oxide (rust)

in the presence of water, oxygen and ions (Satish Kumar et al, 2003).

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There are material which are non steel that widely use in the engineering field.

The non steel material is important is producing a part that need high ductility and low

strength. One of the example of non steel material is aluminum. Aluminum has an ability

of being extruded into complex shapes to exact tolerances. Aluminum also has been

successfully formed into literally thousands of unique profiles, each one able to meet a

number of specific structural and aesthetic requirements. It is this capability to provide

simple elegant solutions to extremely complex design problems that has led to

aluminum's enduring appeal.

There are method to change the material property without changing the shape.

The method is called a heat treatment method. There are 3 most common method used in

heat treatment which is annealing, quenching in water and also quenching in water. The

heat treatment is use in changing the microstructure of the material from ductile to brittle

phase. Heat treatment uses phase transformation during heating and cooling to change a

microstructure in a solid state.

There are some test that can be done to know the strength of the material by

using fatigue test method. By undergo the fatigue test, the cycle of where the material

will be fail can be known. To know the actual fatigue life of the material is mostly

impossible. The engineer has developed a method can be use to predict the fatigue life of

the material. The method is called a fatigue test.

1.2 PROBLEM STATEMENT

Low carbon steel is the most common type of steel used for a general purpose. It

is the cheapest steel among the other steel but has lack of hardenability due to

composition of carbon which is only 0.3%. The manufacturer try to find a way in

manipulating this cheapest carbon steel to increase the application by using the same

material to reduce their operation cost. Low carbon steel can be used to manufacture a

wide range of manufactured goods like home appliances and ship sides to low carbon

steel wire and tin plates.

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Aluminum alloys with a wide range of properties are used in engineering

structures. Aluminum alloys are used widely in aircraft due to their high strength-to-

weight ratio but pure aluminum metal is much too soft for such uses, and it does not

have higher tensile strength that is needed for airplanes and helicopters.

Each material has an unpredictable fatigue which they can fail at any time. The

failure of the material is a dangerous when its relating to the human life for example the

blade fan of the airplane. The fail of the fan blade will make the plane fail to operate

normally and can cause an accident.

1.3 OBJECTIVE

1. To study the fatigue life predictions of a different material. Two types of

specimen is taken which is low carbon steel and also aluminum.

2. To investigate the effect of heat treatment on the fatigue life of low carbon steel

and aluminum alloy.

1.4 SCOPE OF PROJECT

The project is focusing on the fatigue life prediction of low carbon steel and

aluminum. The scope of this project is including :

a) The preparation of the raw material by using the band saw machine

b) The machining specimen for the required shape using the Lathe machine

c) The material undergo the heat treatment which is annealing and quenching

d) The microstructure of the material is analyze using optical microscope

f) The fatigue test is undergo to find the fatigue life prediction of different material

g) The surface fracture of the failed fatigue material is analyze

CHAPTER 2

LITERATURE REVIEW

2.0 INTRODUCTION OF STEEL

Steel is a family of materials that is derived from ores that are rich in iron,

abundant in the Earth’s crust and which are easily reduced by hot carbon to yield iron.

Steels are very versatile. They can be formed into desired shapes by plastic deformation

produced by processes such as rolling and forging (Lesliw,2007). They also can be

treated to give them a wide range of mechanical properties which enable them to be used

for an enormous number of applications. Indeed, steel is wide use in our everyday life

including construction, automotive industry and many manufacturing industry.

There are various type of steel in the industry. Every type of the steel has their

unique properties. The different type of steel is use in a different type of application. The

application is divided into categories which is light use, medium use and heavy use.

The steel can be divided into two main group which is plain carbon steel and

alloy steel. The Table 2.1 show the commonly encountered classes of iron and steel. It

show the typical user for different steel and the source strength of steel.

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Table 2.1 : Class of steel

Class Distinguish feature Typical user Source of strength

Cast iron More than 2 % of C and

1 to 3% of Si

Pipes, valve,

gear, engine

block

Ferrite-pearlite structure as

effected by free graphite

Plain-

carbon

steel

Principle alloying

element is carbon up to

1%

Structural and

machining part

Ferrite-pearlite structure if

low carbon; quenching and

tempering if medium to

high carbon

Low-alloy

steel

Metallic element total up

to 5%

High strength

structural and

machine part

Grain refinement,

precipitation, and solid

solution if low carbon;

otherwise quenching and

tempering

Stainless

steel

At least 10% of Cr, do

not rust

Corrosion

resistant, piping

and nuts and

bolt

Quenching and tempering

if < 15% Cr and low Ni;

cold work or precipitation

Tool steel Heat treatable to high

hardness and wear

resistance

Cutters, drill bit Quenching and tempering

Source : Dowling,1999

The table has classified the different between the type of steel. The steel can be

differentiate by the chemical composition in the material. Every type of material has

their different mechanical properties for a different purpose.

2.2 ALUMINUM IN ENGINEERING FIELD

Aluminum is the most abundant metallic element, and the third constituent of the

earth’s crust. Aluminum occurs many in the environment, in salts and oxides forms.

Because of its physical and chemical properties, aluminum metal and compounds have a

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wide variety of uses: building, transportation, food packaging, beverage cans, cooking

utensils, food additives, medicines, surgery materials, cosmetics, water purification

(Gourier-Frery et al, 2004).

Aluminum is a very light weight material yet has a high strength. In the

investigation on aluminum automotive engineering in German show that aluminum

cover nearly the whole range of semi-finished product and casting as show in Figure 2.1

(Jirang et al, 2009).

Vehicle design for environment has been considered by automotive

manufacturing and research. Based on the weight reduction concept, some of basic idea

should be considered such as designing key structural component for prime alloy with a

maximum property to mass ratio, minimizing the number of material or alloy in one part

and choosing standard alloying element (Jirang et al, 2009).

2.3 MICROSTRUCTURE OF STEEL

Steel is the common building material use in the construction industry. It primary

purpose is to form a skeleton for a building or structure. Steel was made from an iron

with addition of carbon in it. Because the influence of carbon on mechanical properties

of iron is much more than other alloying elements. The atomic diameter of carbon is less

that interstice between iron and atoms and carbon goes into solid solution of iron. As

carbon dissolves in the interstices, it distorts the original crystal lattice iron (Satish

Kumar et al, 2003).

The distortion of the crystal lattice have effect the external applied strain to the

crystal lattice and blocking it. This result the mechanical strength is increase. When the

adding much more of carbon will result in more distortion of the crystal lattice and

increasing in its mechanical strength. Unfortunately, the increasing of mechanical

strength has effect the other important property of the iron which called ductility.

Ductility is define as an ability of the iron to undergo large plastic deformation

(Roylance, 2001).

The addition of carbon is not the only way to increase the mechanical strength,

there are another way even without adding another composition of carbon. This process

is called heat treatment process. T

temperature and been cool down by annealing or quenching. The iron

equilibrium diagram is a plot of transformation of iron with respect to carbon content

and temperature. This diagram is also call

Figure 2.2 (Satish Kumar et al, 2003).

as an ability of the iron to undergo large plastic deformation

Figure 2.1 : Crystal lattice structure

Source : Dimitri,2012

The addition of carbon is not the only way to increase the mechanical strength,

there are another way even without adding another composition of carbon. This process

is called heat treatment process. This process is undergo with heat the iron to certain

temperature and been cool down by annealing or quenching. The iron

equilibrium diagram is a plot of transformation of iron with respect to carbon content

and temperature. This diagram is also called iron-iron carbon phase diagram

Satish Kumar et al, 2003).

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as an ability of the iron to undergo large plastic deformation

The addition of carbon is not the only way to increase the mechanical strength,

there are another way even without adding another composition of carbon. This process

his process is undergo with heat the iron to certain

temperature and been cool down by annealing or quenching. The iron-carbon

equilibrium diagram is a plot of transformation of iron with respect to carbon content

iron carbon phase diagram shown in

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Figure 2.2 : Iron carbon phase diagram by mass

Source : http://www.calphad.com/iron-carbon.html

1) Ferrite (α): Virtually pure iron with body centered cubic crystal structure (bcc). It is

stable at all temperatures up to 900C. The carbon solubility in ferrite depends upon the

temperature; the maximum being 0.02% at 723oC.

2) Cementite: Iron carbide (Fe3C), a compound iron and carbon containing 6.67%

carbon by weight.

3) Pearlite: A fine mixture of ferrite and cementite arranged in lamellar form. It is stable

at all temperatures below 723oC.

4) Austenite (γ): Austenite is a face centred cubic structure (fcc). It is stable at

temperatures above 723oC depending upon carbon content. It can dissolve up to 2%

carbon.

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2.4 HEAT TREATMENT

Heat treatment is a process to changing the mechanical properties of the material

without changing the shape. Heat treatment of carbon steel component is done to take

the advantages of crystalline defect and their effect and thus obtain a certain desirable

properties or condition. The differences in mechanical properties of a given steel are the

result of different microstructures formed during cooling.

According to I.F Machado, the microstructure of AISI 1020 steel in the as-

receive condition is show in Figure 2.3 below. In this steel, pearlite was observe in the

microstructure and its volumetric fraction of about 40% volume was related to the mass

carbon percentage in the steel (Machado,2006).

Figure 2.3 : Microstructure as-receive of AISI 1020

Source : Machado,2006

The result of Vickers microhardness (20 N) of the sample of AISI 1020 in the as-

receive condition, heat-treated at 750 ͦ C for 150 min and the at 750 degree C for 150

min by applying 27 V were display in the Table 2.2

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Table 2.2 : Vickers microhardness of AISI 1020

Condition Time(min) V A HV 2

1020 AS 0 0 0 191.7 ± 1.5

1020 HTQ 150 0 0 254.3 ± 10.0

1020 HTQ 58 150 27 5.8 447.0 ± 21.2

2.5 HARDENING OF MATERIAL

Hardening is only possible via heat treatment on medium to high carbon steels,

the metals are heated to certain temperatures depending on their carbon content (780°C

to 850°C) then cooled quickly usually by quenching the metals in water or oil, the reason

the metals are heated to these temperatures called their ‘austenitic crystal phase’ is

because the crystal structures of the metals can then start to alter, forming bonds to

create cementite as the carbon diffuses which is a very hard and brittle material.

Figure 2.4 : Microstructure of the AISI 1020 steel heat treated

Source : Machado,2006

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2.6 INTRODUCTION OF FATIGUE LIFE

The engineering material scope is mostly concentrated on the failure of

component and static loading in an overload situation. In this real world, failure always

occurs at stresses much lower that material ultimate strength. This phenomena of

component which is failing at relatively low strength become quite a surprise for some

engineers in the early time of engineering material component design. More worst for

this problem is the material did not give anything sign of fatigue or tiredness. The

fatigue term which has been justified for this aspect of metal behavior at a repeated cycle

is a bit misleading as the material would not regain its strength after resting, but will

actually remember the previous stress cycle.

2.7 FATIGUE BACKGROUND AND HISTORY

One of the first people trying to figure out the fatigue problem was a railway

engineer in Germany, August Wholer. Wholer use full scale railway axles and some

other test and drew up a stress versus stress cycle to failure curve, S-N curve. Wholer

most important curve is shown in the Figure 2.5 and also found that the steel exhibit

something called endurance limit, which will result in no damage below this stress value

(Wholer, 1997).

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Figure 2.5 : S-N diagram by Wholer

Source : Wholer,1997

2.8 FATIGUE TEST

A perusal of the broken parts in almost any scrap yard will reveal that the

majority of failures occur at stresses below the yield strength. This is a result of the

phenomenon called fatigue which has been estimated to be responsible for up to 90% of

the in-service part failures which occur in industry.

If a bar of steel is repeatedly loaded and unloaded at about 85% of its yield

strength, it will ultimately fail in fatigue if it is loaded through enough cycles. Also, even

though steel usually elongates approximately 30% in a typical tensile test, almost no

elongation is evident in the appearance of fatigue fractures. Basic fatigue testing

involves the preparation of carefully polished test specimens (surface flaws are stress

concentrators) which are cycled to failure at various values of constant amplitude

alternating stress levels (Berman, 2007).

The data are transfer into an alternating Stress, S, verses Number of cycles to

failure, N, curve which is generally referred to as a material’s S-N curve. As one would

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expect, the curves clearly show that a low number of cycles are needed to cause fatigue

failures at high stress levels while low stress levels can result in sudden, unexpected

failures after a large number of cycles

2.9 S-N CURVE

Before the fatigue process microstructure understanding was developed,

engineers had developed empirical means of quantifying the fatigue process and design

against it. After that, the most important concept is the S-N curve, for example the one

shown in Figure 2.6 in which the constant cyclic stress amplitude, S is applied to a

specimen and the number of loading cycle, N until the specimen fails was obtain. Many

of cycle needed, even millions of cycle might be required to cause failure at lower

loading levels.

Figure 2.6 : Curve for aluminum and low carbon steel

Source : Jirang et al. 2009

In some of other material, notably ferrous allow, the S-N curve was flattens out

eventually, so that below certain limit ϭe failure does not occur no matter how long the